This invention relates to improvements in screw-type dental implants and, in particular, to reducing the friction between the main body of such an implant and the side walls of a bore provided in living jawbone when the implant is screwed into that bore.
Screw-type dental implants are widely used and have been known for a number of years. They are made in two general types. The first type is a self-tapping implant, in that it can be threaded into a pre-drilled bore in a jawbone without pre-tapping the bore. The second type is a non-self-tapping implant that requires pre-tapping of the bore. In either type, the implant has a generally cylindrical main body which bears one or more external screw threads on its outer surface. These external thread(s) engage corresponding internal thread(s) cut into the wall of the bore to provide initial stabilization of the implant in the bore.
A problem commonly encountered is the friction between the implant and the bone walls defining the bore. The friction is proportional to the penetration depth of the implant into the bone, the diameter of the bore, and the hardness of the bone at the site of the bore. The torque that must be applied to insert the implant into the bore is proportional to the friction. High torque puts strains on the implant, on the tools used to place the implant in the bore, and on the bone. Furthermore, in cases where high torque is required to insert the implant, there is a greater risk of damage to the implant, the tools, and the bone. Consequently, there is a continuing need to design a screw-type dental implant which minimizes the torque needed to install it into living jawbone.
In the design of screw-type dental implants as presently practiced, the main body of the implant is generally cylindrical. The thread peaks and thread roots (troughs) are each on the locus of a cylinder with each cylinder being concentric about the cylinder axis of the main body.
It is a primary object of this invention to provide an improved dental implant that reduces the torque required to install the implant into the bore in the jawbone and fix it in place in that bore.
Another object of the invention is to provide an improved screw-type dental implant that reduces the torque required to install the implant by reducing the friction between the implant and the sidewalls of the bore. A related object is to reduce the time and effort required to install the implant.
An additional object of the invention is to provide an improved screw-type dental implant that will resist forces tending to unscrew it from the bore after it has been installed.
Other objects and advantages of the invention will become apparent from the following description and the accompanying drawings.
In accordance with the present invention the foregoing objectives are realized by providing an improved screw-type dental implant comprising a generally cylindrical body having a threaded outer surface for securing the implant to the walls of a preformed hole in a jawbone. At least one dimensional characteristic of the body is varied with respect to its azimuthal position around the cylinder axis so as reduce the overall frictional contact between the implant body and the walls of the bore during installation of the implant. The variance in this dimensional characteristic also serves to resist turning of the body in the bore after the bone in the side walls of the bore has grown onto the implant body in the normal healing process. Examples of such a dimensional characteristic include:
a) the radius of the locus of the peaks of the threads;
b) the radius of the locus of the troughs of the threads;
c) thickness of the threads; and
d) angle between the faces of the threads.
An embodiment of the invention may employ these and other characteristics variably according to the invention, singly or in combination with one or more of the others. The variation employed can be cyclical or random around the cylinder axis. It can be synchronous or it can progress or regress with respect to the axis as its proceeds along the axis from one end of the body toward the other end.
Generally, the invention may provide an implant in which some portions of (for example) the peaks or troughs of the threads are on the original cylinder lacking the varied radius while other portions of the same characteristic are within that cylinder so that they make less or no contact with the walls of the hole. This design has two effects. First, by reducing the area of implant body that makes contact with the walls of the bore, the friction between the implant and the bone during installation of the implant is reduced. And second, after the bone has grown during healing to touch the implant body around the irregular (non-circular) portions thereof, the implant body resists turning in the bone more than would a typical implant having a cylindrical body lacking the radial-dimension variations of the invention.
Similar considerations apply to varying the thickness of the threads with respect to azimuthal position around the cylinder axis. One technique for varying the radius of the locus of the thread peaks is also effective to vary the thickness of the threads synchronously with variation in the radius, so that these two characteristics can be employed simultaneously with one manufacturing process step.